Effect of Eucalyptus Globulus Wood Density on Papermaking Potential

peer-reviewed papermaking Effect of Eucalyptus globulus wood density on papermaking potential

António Santos, Maria Emília Amaral, Álvaro Vaz, Ofélia Anjos, and Rogério Simões

ABSTRACT: It is well documented that the characteristics of raw materials determine the papermaking potential of the pulp. The variability of the wood used by the pulp mills is extremely wide. We report on the behavior of three Eucalyptus globulus wood chip samples with basic densities of 0.467, 0.537, and 0.600 g/cm3, in kraft cooking and papermaking. The pulp yield range of 49%–58.7% was attributed to the different wood chemical composition, in particular to the lignin content and relative proportion of cellulose and hemicelluloses. The morphological characteristics of the pulp fibers were also markedly different. The average fiber length is 0.71, 0.80, and 0.85 mm, respectively for the E. globulus of low, intermediate, and high wood basic density. The pulp fibers from the lowest density wood exhibit very high wet fiber flexibility, while those from the highest density wood exhibit rigid behavior. Using this structural property as reference, the corresponding papers are stronger, but exhibit lower light scattering coeffi- cients than those from the lowest density wood. Application: Understanding the morphological characteristics of the E. globulus wood fibers in tree selection and genetic improvement programs, in addition to the wood density and pulp yield, can help papermakers to avoid negative impact on light scattering coefficient and refining energy consumption.

leached Eucalyptus globulus kraft pulp has a strong optimization efforts should also consider fiber characteristics Bmarket position for the production of printing and such as fiber wall thickness, fiber width, and fiber length. writing papers due to its strength, bulk, opacity, and Several papers were published recently concerning the rela- smoothness [1, 2]. This performance is mainly due to the tionships between wood basic density and fiber and pulp morphological characteristics of the pulp fibers, in par- characteristics [5, 9]. Most of the work in this area analyzed ticular its high Runkel ratio (twice the fiber wall thickness dozens of wood samples and estimated their papermaking divided by the lumen diameter) and the relatively low pulp potential based on the unrefined or gently refined pulps. This fiber width. The low fiber length also leads to a very high is a good strategy for correlation assessment but it does not number of fibers per gram, which confers good formation consider the impact of beating on paper properties. to the papers [3]. The number of fibers per gram, the high We selected three E. globulus wood samples representative specific surface area, and the relatively high pulp fiber of two clone stands and current industrial raw material, with rigidity lead to papers with high bulk and opacity. The markedly different wood basic densities, to evaluate the vari- paper exhibits good strength properties, at the expense of ability of E. globulus pulp fiber characteristics and their influ- a relatively high-energy consumption in beating [2]. ence on papermaking potential. The pulp fibers have similar Although the general performance of E. globulus grown fiber width but markedly different fiber wall thickness, which in Portugal for printing and writing paper production is very enabled us to investigate its influence on beating response. good, it is of technical and scientific interest to evaluate the influence of the morphological variability of E. globulus fi- EXPERIMENTAL bers on their performance in the papermaking process and Table I shows the provenance, climate conditions, mean age, on the final paper properties. It is well known that both the and basic density of the two wood samples coming from two pulping processes and the raw material affect pulp fiber prop- clone stands grown in Portugal. The third sample was an in- erties. However, for a given pulping process, raw material is dustrial chip sample from a Portuguese pulp mill, with a basic the main factor determining pulp fiber properties [2–4]. density of 0.537 g/cm3. The samples were previously screened It is also well documented that there is considerable fiber to remove over-thickness chips (>8 mm) and fines. We deter- morphology variability within trees, between trees within a mined the cross-section dimensions of the vegetal cells in the stand, and between trees from different stands [5, 6] because wood samples by image analysis using the Qwin 500 system of genetic variability, soil-related and climatic conditions, and from Leica Microsystems® (Wetzlar, Germany). For each wood cambium age. This variability has been exploited in genetic sample, four resin-embedded representative samples were improvement programs for different species and also for E. prepared and polished to observe in a reflection microscope. globulus [7, 8]. The main objective has been to increase pulp Five images from each preparation were recorded with a mag- production per cubic meter of wood, which is associated with nification of 50X, accounting for 20 images per wood sample. the increase of wood basic density and pulp yield. However, About 20 fibers were measured (fiber wall thickness and fiber

may 2008 | TAPPI JOURNAL 25 papermaking

Rainfall, Mean Age, Basic density, Site mm/yr Altitude, m temperature, ºC year Tree g/cm3 Odemira E. globulus–LD 635 70 15.0 7 Clone 0.467 (37º36’N; 8º 39’W) E. globulus– ID Pulp mill - - - 10 Industrial 0.537 Mortágua E. globulus–HD 1255 250 14.9 11 Clone 0.600 (40º 24’N; 8º 09’W) I. Location of the sites and characteristics of the raw materials: low density (LD), intermediate density (ID), high density (HD). width in tangential direction) in each image, providing nearly Wood basic density (g/cm3) 400 measurements for each property and each sample. We 0.600 0.467 (LD) 0.537 (ID) also evaluated the percentage of vessel area. (HD) The wood basic density was determined according to Effective alkali charge 18.7 18.7 17.9 TAPPI 258 om-94 [Basic density and moisture content of pulp- (%, as NaOH) wood]. Representative materials were ground and samples Sulfidity (%) 30 30 30 prepared for lignin and extractives contents determination according to TAPPI 222 om-88 and TAPPI 204 om-88 [Acid- Liquid/wood ratio 4:1 4:1 4:1 insoluble lignin in wood and pulp; Solvent extractives of Time to temperature wood and pulp] (successively with dichloromethane, ethanol, (min) 90 90 90 and water), respectively. Time at temperature 60 58 45 The wood chips underwent a conventional kraft cooking (160ºC) (min) process under the following reaction conditions: effective Pulp yield 49.0 52.4 58.7 alkali charge, variable; sulfidity index, 30%; liquor:wood (%, on wood) ratio, 4:1; time to temperature, 90 min; time at temperature Rejects (%, on wood) 0.2 3.0 0.9 (160ºC), variable. Experiments were carried out with 1000 g o.d. of wood in a forced circulation digester. The cooked Kappa number 15.3 16.2 14.0 chips were disintegrated, washed, and screened on an L&W Viscosity, cm3.g-1 screen with 0.3 mm slot width. The accepted material was unbleached pulps 942 1053 1274 collected on a 200-mesh screen. The screened and total yields 3 -1 Viscosity, cm .g 855 982 945 were gravimetrically determined. Kappa number and pulp bleached pulps viscosity were evaluated according to the ISO 302 [Pulps - II. Cooking conditions and results. Determination of kappa number] and ISO 5351/1 standard methods [Cellulose in dilute solutions - Determination of lim- determined according to the Silvy et al. procedure [13], for the iting viscosity number - Part 1: Method in cupri-ethylene-di- suspension with and without fines. Fines were removed in the amine (CED) solution]. The brown stock was bleached ac- Bauer-McNett apparatus, using a 100-mesh screen. We prepared cording to the D0E1D1E2D2 sequence, using a kappa factor of paper hand sheets according to Scan-C 26:76 and tested their

0.2 in the D0 stage and the same charges and reaction condi- structural, mechanical, and optical properties. tions in the remaining stages. The neutral sugar composition of the woods and pulps RESULTS AND DISCUSSION were determined after acid hydrolysis by gas chromatography Cooking analysis, according to published procedures [10, 11]. The mor- The wood basic density values obtained for E. globulus sam- phological properties of pulp fibers were determined auto- ples were within the usual range reported for this species [7]. matically by image analysis of a diluted suspension (20 mg/L) The cooking conditions required by the three samples to pro- in a flow chamber in Morfi® (TECHPAP, Grenoble, France). duce kraft pulp with kappa number in the range of 14–16 were The pulps were beaten in a PFI mill at 500, 2500, and 4500 significantly different (Table II). In particular, the wood revolutions under a refining intensity of 3.33 N/mm. Wet fiber sample with the highest basic density required the mildest flexibility (WFF) was determined according to the Steadman reaction conditions and led to a pulp yield nearly 10 points and Luner procedure [12], using CyberFlex® (CyberMetrics, higher than that exhibited by the wood sample with the low- Roswell, Georgia, USA) equipment in a fine free suspension. est wood basic density. These differences cannot be attrib- In summary, a very thin and oriented fiber network was uted to the casual losses of fine elements, such as vessels, in formed on a wire of a very small head-box and transferred to a pulp collection after cooking because a 200-mesh screen was glass slide with wires under controlled pressure conditions [12]. used and the vessel dimensions and its content in the woods The same equipment and procedure, this time using glass slides were not so different (data not shown). According to our pre- without wires, were used to measure the relative bonded area vious experience the standard deviation of the pulp yield is (RBA) of the wet fibers. The water retention value (WRV) was close to unity. The pulp yield variability is in good agreement

26 TAPPI JOURNAL | may 2008 papermaking

Lignin Extract Total the other hand, E. globulus–LD pulp ex- content (%) Dichloromethane Ethanol Water extractives hibited the lowest pulp viscosity before and after bleaching. Considering the E. globulus–LD 21.5 0.35 0.34 1.91 2.6 (±1.0) (±0.5) dominant contribution of cellulose for 20.0 4.7 the viscosity values, 1% less in cellulose E. globulus–ID (±0.9) 1.58 1.78 1.37 (±0.6) content cannot justify the differences 18.0 2.8 E. globulus– HD (±1.2) 0.17 1.12 1.45 (±0.2) observed in pulp viscosity and they can III. Lignin and extractives contents. tentatively be attributed to the higher cooking time and the lower tree age. Glucose Xylose Galactose Mannose Arabinose WOOD AND FIBER E. globulus–LD 65.7 30.2 1.9 1.3 0.8 wood PROPERTIES E. globulus–HD Table V shows the biometric charac- wood 67.2 28.5 1.8 1.8 0.6 teristics of the fibers for the three un- E. globulus–LD pulp 76.8 22.6 0.2 0.2 0.1 beaten pulps. The following conclusions can be drawn: E. globulus–HD 77.6 21.6 0.4 0.2 0.2 pulp 1. E. globulus–HD pulp, produced from IV. Neutral sugar composition of E. globulus–HD and E. globulus–LD woods and the wood of the highest density, ex- bleached pulps (molar proportions, %). hibits fibers with an average length of 0.85 mm, which is 20% higher than with reported data [7, 14]. Bleaching that exhibited by the pulp with the The very high pulp yield exhibited No differences were detected regarding lowest pulp yield, coming from the by high-density (HD) E. globulus can be pulp bleachability, and the yield losses wood with the lowest basic density attributed to both the low lignin content were close to 3% for the three pulps. The (0.467 g/cm3) and the tree stand of (Table III) and the high relative con- analysis of the chemical composition of the lowest age; tent of cellulose in the carbohydrate the bleached pulps in terms of sugar pro- 2. E. globulus–HD pulp fibers are only fraction of this wood (Table IV). Con- portion shows that the HD pulp exhib- slightly wider than those of E. globu- sidering that the large majority of the ited about 1% higher cellulose content lus–LD, but exhibit a fiber coarseness, carbohydrates in wood and particularly than the low-density (LD) pulp. We ob- which is close to 40% higher; and in pulps are glucose and xylose, it seems served the same order of magnitude for 3. The pulp fibers produced from the in- acceptable to assign the glucose to cel- the corresponding wood samples. The dustrial chip sample exhibit interme- lulose and xylose to xylan. The other higher retention of cellulose and xylan diate morphological characteristics. wood samples exhibit lower pulp yields in the HD pulp, in comparison with the than E. globulus–HD, as a consequence LD pulp, was in accordance with the The fiber length and coarseness cor- of the wood chemical composition and milder reaction conditions required by relate linearly with the wood basic den- the required cooking conditions. the HD wood (see Table II; the residual sity. The coarseness differences between alkali is close to 4 g/L, for all cooks). On the HD and LD pulps cannot be only at-

Length, Coarseness Fibers/gram Fiber width (µm) length-weighted (mm) (mg/m) x 10-6 LD (0.467 g/cm3) 18.3 (±0.1) 0.711 (±0.003) 0.051 (±0.001) 31.9 (±0.6) ID (0.537 g/cm3) 18.6 (±0.1) 0.805 (±0.005) 0.061 (±0.001) 23.6 (±0.5) HD (0.600 g/cm3) 19.3 (±0.1) 0.853 (±0.005) 0.072 (±0.003) 19.2 (±0.8) V. Fiber characteristics of unbeaten pulps (mean ± standard deviation).

LD (0.467 g/cm3) ID (0.537 g/cm3) HD (0.600 g/cm3)

Fiber wall Fiber width Fiber wall Fiber width Fiber wall Fiber width thickness (tangential) thickness (tangential) thickness (tangential) (µm) (µm) (µm) (µm) (µm) (µm) Mean 2.67 12.13 3.18 13.16 3.43 12.32 SD 0.56 2.08 0.62 1.83 0.58 1.51 Maximum 3.11 14.63 4.12 16.67 4.47 14.90 Minimum 1.81 9.72 2.14 9.40 2.18 9.73

VI. Wood fiber characteristics (SD = standard deviation).

may 2008 | TAPPI JOURNAL 27 papermaking

3. Evolution of the Schopper Riegler degree (ºSR,s=0.5) with beating, for the three E. globulus pulps. 1. Correlation between wood basic density and fiber wall thickness.

4. Evolution of WRV (s=3) with (CF) and without (SF) fines with beating, for the LD (0.467 g/cm3) and HD (0.600 g/cm3) E. globulus pulps. pulp fibers coming from the wood sample with the lowest basic density (LD–0.467 g/cm3) are, even without beating, very flexible, while those coming from the wood samples with the highest basic density (HD–0.600 g/cm3) exhibit very low values of flexibility without beating. This unit operation has a tremendous positive impact on WFF. However, even for the highest beating level (4500 revolutions in PFI mill), the fibers from E. globulus–HD are more rigid than E. globulus– 2. Evolution of wet fiber flexibility (WFF, top) and relative bonded LD pulp fibers. Figure 2 bottom represents the relative bond- area (RBA, bottom) with beating, for the three samples of E. ed area, measured in individual wet fibers put on a slide, rep- globulus (standard deviation (s): WFF = 1; RBA=0.9) resenting the ratio between the area effectively in contact with the slide and the projected area of the fiber. The differ- tributed to the differences in pulp yield, which reaches 20%. ences between the pulp fibers are very large at the beginning The morphological characteristics of the wood cells should and decrease with beating, but significant differences remain also be considered. In fact, the microscopic analysis of the even at 4500 revolutions in the PFI mill. cross-section of the wood fibers (Table VI) revealed that E. globulus–HD has a mean fiber wall thickness of 3.4 µm, while PAPERMAKING POTENTIAL E. globulus–LD has only 2.7 µm; on the contrary, the average Figure 3 plots the mean value evolution of drainability resis- fiber width (tangential) is close for the three samples. There- tance for the three pulps. For unbeaten pulps, the fibers from E. fore, the objective of producing pulps with markedly different globulus–HD (0.600 g/cm3) exhibit the lowest drainability resis- morphological properties was attained. Table VI also illustrates tance, while E. globulus–LD (0.467 g/cm3) pulp shows the high- the wide range of variation for both the fiber wall thickness est value. These results are expected considering the morpho- and the fiber width. Moreover, a good correlation between the logical properties of the fibers. The three pulps exhibit fibers wood basic density and the fiber wall thickness was observed with similar width, but the very low fiber wall thickness of E. (Fig. 1), as expected and previously reported [9]. globulus–LD pulp fibers leads to a very high specific surface area The wet fiber flexibility (WFF) measurements highlight (m2/g of pulp) and, consequently, high drainage resistance. The the considerable differences between the three bleached pulp contrary occurs for E. globulus–HD fibers, which are coarse but fibers and also reveal the effects of beating and fiber morphol- exhibit the highest rate of drainage resistance development. The ogy on the fiber flexibility development (Fig. 2 top). The microscope observation of the pulp suspensions, under dark

28 TAPPI JOURNAL | may 2008 papermaking

5. Evolution of paper density (s=0.01) with beating, for the three E. globulus pulps.

6. Correlation between paper density and wood basic density. 7. Evolution of tensile index (s=5) as a function of PFI revolutions (top) and paper density (bottom). field, showed that E. globulus–HD pulp fibers develop higher external fibrillation than E. globulus–LD. nificant throughout the range of this property. The different beating development is also revealed in the The paper density has a strong influence on paper perfor- water retention value (WRV) of the pulp suspension with mance and its value, as well as those for other properties, fines (Fig. 4). The WRV for the pulp suspension without measured for unbeaten or gentle beaten pulps, has been used fines revealed that E. globulus–HD pulp fibers show, in gen- as an indicator of papermaking potential of the wood samples. eral, slightly lower water retention than E. globulus–LD pulp, Moreover, these values can also be correlated with wood throughout the refining period (Fig. 4), despite their higher properties or some fiber properties. Figure 6 shows the very external fibrillation. Conjugation of previous results suggests good negative correlation between the paper density at 500 lower swelling and higher external fibrillation aptitude of E. PFI revolutions and the wood basic density. Similar correla- globulus–HD pulp. Seth [15], working with softwood pulps tions were also observed between paper density and fiber with very different coarseness, reported significantly higher wall thickness or fiber coarseness. However, the diverse re- external fibrillation for the coarse fibers at 6000 PFI revolu- sponses of the different fibers in beating should also be con- tions. The influence of fines on WRV measurements is also sidered in order to have a more realistic picture of the paper- remarkable for both pulps (Fig. 4). making potential of the wood samples. Figure 5 reveals that E. globulus–HD pulp exhibits As expected from the paper density data (and correspond- paper density values markedly lower than the other two ing paper porosity), E. globulus–HD exhibits higher air perme- pulps for all the beating range, but the differences between ability than the other pulp samples, at a given beating energy. the pulps are significantly attenuated with beating. This ob- Paper smoothness is markedly higher for E. globulus–LD pulp, servation is explained by the markedly different evolution at a given refining level, but there are no significant differenc- with beating of wet fiber flexibility and relative bonded area es when the comparison is made at a given paper density. (Fig. 2) of the different pulp fibers. On the other hand, even Regarding mechanical properties, E. globulus–LD pulp ex- at 4500 PFI revolutions, where drainage resistance of E. glob- hibits higher tensile (Fig. 7 top) and burst strengths than E. ulus–HD pulp is significantly higher than the other corre- globulus–HD, at a given PFI revolutions, in accordance with sponding suspensions, the paper density remains significant- its higher paper density. Considering again the tensile values ly lower than E. globulus–LD pulp, which is a very important at 500 PFI revolutions, a negative correlation between this consequence of fiber morphology. Furthermore, around 500 property and the wood basic density, fiber wall thickness or and 2500 PFI revolutions were required, respectively, for E. coarseness was observed. However, the beating has an impor- globulus–LD and E. globulus–HD to reach a paper density of tant impact on tensile strength and the differences between 0.75 g/cm3. The differences are markedly reduced when the the pulps decrease with beating, particularly for E globulus- reference is tensile strength (Fig. 7 top), but remain sig- ID, as Fig. 7 (top) shows. Furthermore, the representation of

may 2008 | TAPPI JOURNAL 29 papermaking

8. Photomicrographs (magnification 50x) of the HD pulp beaten at 2500 revolutions (left) and LD pulp beaten at 500 revolutions 10. Evolution of tear index as a function of tensile index. (right), to achieve a paper density close to 0.77 g/cm3. tensile strength as a function of paper density reveals that E. globulus–HD pulp can produce stronger papers than the other pulps. These results are mainly a natural consequence of the higher inter-fiber bonding developed by E. globulus–HD and E. globulus–ID pulp fibers compared with E. globulus–LD pulp fibers, at a given paper density. Figure 8 represents the photomicrographs of the pulp fibers (E. globulus–HD and E. globulus–LD) corresponding to the papers with similar densities (≈ 0.77 g/cm3). The much higher external fibrillation on E. globulus–HD pulp fibers is evident. However, the better performance of E. globulus–HD is achieved at the expense of higher energy consumption in beating. For the pulps under evaluation, the fiber length and zero-span tensile strength have only minor effects on the relationship between tensile and paper density. The bonding between the fibers should control the paper strength at this level. The zero-span tensile strength data show the slightly superior performance of E. globulus– HD compared with E. globulus–LD in the dry tests (195 vs. 187 N.m/g, at 500 PFI revolutions); the difference reaches 10%

11. Light scattering coefficient (s=0.7) vs. paper density (top) and mechanical strength (bottom).

when the comparison is based on the corresponding wet tests (170 vs. 152 N.m/g, at 500 PFI revolutions). At least three characteristics [16, 17] could be cited to explain the superiority of E. globulus–HD pulp: lower fibril angle; lesser weak points in the fiber wall, such as kinks and nodes; and higher pulp viscosity, which is the most obvious (Table II). Figure 9 illustrates that the pulp coming from the wood with ID exhibits superior performance relative to the other two pulps. Number of fibers per gram, fiber length, intrinsic fiber strength, and inter-fiber bonds seem to be favorably com- bined in E. globulus–ID pulp. Despite the highest values of intrinsic fiber strength and fiber length (Table V) for E. globulus–HD pulp fibers, the low number of fibers per gram of pulp leads to relatively low tearing resistance. The superior performance of E. globulus–ID is also evident in Fig. 10, where tear index is reported as a function of tensile index. In Fig. 11, light scattering coefficient, a very important char- 9. Evolution of tear index (s=1) as a function of PFI revolutions acteristic for printing and writing papers, is represented as a (top) and paper density (bottom). function of paper density. E. globulus–HD pulp exhibits the

30 TAPPI JOURNAL | may 2008 papermaking

, the paper produced from E. globulus–HD is bulkier, but the light scattering coefficient is lower and the corresponding pulp suspension drain slower than E. globulus–LD. The wood chip sample with intermediate density (0.537 g/cm3) produced hand sheets that are somewhat denser than E. globulus–HD, but the suspension drains better and the paper exhibits very good light scattering coefficient. The pulping data are favorable to the clone with the wood basic density of 0.600 g/cm3, but the papermaking results indicate that poor light scattering ability and high energy consumption in refining of these pulp fibers are important drawbacks. TJ

ACKNOWLEDGEMENTS We thank the Ministry of Science and Superior Education, through Program POCTI and Project AGR/42594/2001 for the scholarship granted to António J.A. Santos; RAIZ (Instituto de Investigação da Floresta e Papel) for providing chip samples; and Carlos Pascoal Neto (Universidade de Aveiro) for sugar determination.

12. Paper density (top) and ºSR (bottom) vs. mechanical strength. Received: June 13, 2007 Revised: August 31, 2007 notably lowest light scattering, in good accordance with the Accepted: December 10, 2007 lowest specific surface of these fibers. Even when the geometric average of tensile and tear indexes ( ) is used LITERATURE CITED for comparison, E. globulus–HD compares badly with the other 1. Kibblewhite, R.P., Bawden, A.D., and Hughes, M.C., Appita J. 44(5): pulps in terms of light scattering. On the contrary, Fig. 12 (top) 325(1991). shows that E. globulus–HD can produce bulkier hand sheets 2. Santos, A., Anjos, O., and Simões, R., Appita J. 59(1): 58(2006). than the other pulps, at given paper strength, which is a positive 3. Paavilainen, L., Paperi Puu 82(3): 156(2000). feature. In accordance with bulk, E. globulus–HD pulp exhibits a much higher bending stiffness than E. globulus–LD pulp, at 4. Paavilainen, L., PaperiPuu 71(4): 356(1989). paper strength of 20. However, this is achieved at the expense 5. Downes, G., Evans, R., Wimmer, R., et al., Appita J. 56(3): 221(2003). of higher specific energy consumption in refining and probably 6. Evans, R., Kibblewhite, R.P., and Lausberg, M., Appita J. 52(2): at higher drainage resistance (Fig.12). 132(1999). 7. Valente, C.A., Mendes de Sousa, A.P., Furtado, F.P. et al., Appita J. CONCLUSIONS 45(6): 403(1992). In accordance with their chemical compositions, the three E. 8. Greaves, B.G. and Borralho, N.M.G., Appita J. 49(2): 90(1996). wood chip samples exhibit markedly different behav- globulus 9. Kibblewhite, R.P., Evans, R., and Riddell, M.J.C., iors in the kraft cooking process, in terms of pulp yield and 57th Appita Annual General Conference Proceedings, APPITA, Carlton, chemical consumption. The E. globulus with the highest wood Victoria, Australia, 2003, p. 99. 3 basic densities, 0.600 g/cm , exhibits a much higher pulp yield 10. Neto, C.P., Seca, A., Fradinho, D., et al., Industrial Crops and Products (58.7%) than the E. globulus with the lowest wood basic densi- 5:189(1996). ties (49%). The three chip samples provided pulp fibers with 11. Blakeney, A.B., Harris, P.J., Henry, R.J., et al., Carbohydr. Res. 113(2): markedly different morphological characteristics. The fiber wall 291(1983). thickness and the corresponding coarseness are very different 12. Steadman, R.K. and Luner, P., ESPRA Rep. No. 79, Chap. V, while the fiber width is comparable. The experimental data have Syracuse, New York, USA, 1995. confirmed that the wet fiber flexibility of the unbeaten pulp fi- 13. Silvy, J., Romatier, G., and Chiodi, R., Revue A.T.I.P. 22(1): 31(1968). bers is extremely dependent on the fiber wall thickness and have revealed the different sensitivity of the fibers to beating; the WFF 14. Miranda, I., Tomé, M., and Pereira, H., Appita J. 56(2): 140(2003). of the coarse pulp fibers increase drastically with beating. These 15. Seth, R.S., TAPPI J. 82 (3):147(1999). fibers require more beating energy and develop higher external 16. French, J., Conn, A.B., Batchelor, W.J. et al., Appita J. 53(3): fibrillation. Also, the corresponding pulp suspensions drain slow- 200(2000). er to reach a given paper density although the tensile strength is 17. Leopold, B. and Thorpe, J., Tappi 51(7): 304(1968). substantially higher. At a given paper strength, evaluated as

may 2008 | TAPPI JOURNAL 31 papermaking

insights from the authors showed that wood density variability affects pulp fiber morphology and has an important impact on The high variability of Eucalyptus globulus affects di- beating and paper properties. gester yield and papermaking potential so there is industrial interest to investigate this topic. We were Santos is a scholarship researcher and Amaral and also interested in the relationships between pulp Vaz are auxiliary professors at Universidade de Beira fiber characteristics and paper structure and proper- Interior, Covilhã, Portugal. Anjos is associate professor ties, which is an area we will continue to investigate. at Escola Superior Agrária de Castelo Branco, Castelo External fibrillation evaluation, which was carried Branco, Portugal. Simões is associate professor at out by microscopic observation under dark field, was Universidade de Beira Interior, Covilhã, Portugal; E-mail the most difficult aspect of our work. The research Simões at [email protected].

Santos Amaral Vaz Anjos Simões

Editor’s Note Jan Bottiglieri | Editor, [email protected] Get out there! pring is finally here (yes, I did strong technical program with poster see snow falling a mere two There are plenty of events sessions. The International Conference Sdays ago here at my suburban coming up on the calendar on Nanotechnology for the Forest Prod- Chicago office, but I am dismissing ucts Industry, June 25-27, brings togeth- it as an anomaly.) At TAPPI, that that offer targeted er some of the leading names in the field means we’re all busy working on the technical programs and with five keynote speakers. And TAPPI’s exciting events being offered over the 2008 EPE Conference (August 24-27) next several months. By the time you outstanding opportunities and the 2008 International Bioenergy & read this, PaperCon ’08 will be over; for peer interaction. Bioproducts Conference (August 27-29) but if you were there, I’m sure you’re are scheduled successively in Portland, still feeling energized by the network- Oregon – now that’s “one-stop shop- ing and knowledge that you picked ing up on the calendar that offer target- ping” for all your knowledge needs. up in Dallas. The latest report from ed technical programs and outstanding So (to borrow a line from a cruise HQ is that at least 900 attendees and opportunities for peer interaction. TAP- line commercial) this summer, get out 50 exhibitors are already set to make PI’s 10th Advanced Coating Fundamen- there! TAPPI events offer more than a it a truly dynamic event. tals Symposium, June 11-13, features sunburn by the crowded pool. There are plenty of other events com- some great post-conference tours and a

32 TAPPI JOURNAL | may 2008